fix-1221: offline flag, metadata property nonexistent (#1221)

[ghost]

Summary

--offline flag is not working. #1221

• Problem: nonexistent property prevented any cached package from satisfying.
• Solution: use correct property name from readPackageMetadata

Test plan

$ yarn add [package]
$ rm -rf ./node_modules && rm -f yarn.lock
$ yarn add [package]@version --offline

Improvement

Without version: latest range is used and is not available, this will list the possible versions via the error: Possible versions: ${Object.keys(body.versions).join(', ')}. Possible improvement is to give user option [y/n]-prompt to use latest local version. (out of scope for this PR, should be feature request?)